Ultra-violet lens



May 22, 1962 1Filed Dec. s1, 1958 R. E. TIBBETTS ULTRA-VIOLET LENS SEARCH ROOM 2 Sheets-Sheet l ATTORNEYS United States Patent O 3,035,490 ULTRA-VIOLET LENS Raymond E. Tibbetts, Rochester, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 31, 1958, Ser. No. 784,331 2 Claims. (Cl. 88-57) This invention relates to improvements in optical lenses and more particularly to a high aperture, optical lens corrected for spherical and chromatic aberrations, coma, as-tigmatism, and iield curvature in the xitra-violet range of the electromagnetic spectrum.

Much work has been done with ultra-violet radiation. In the use of ultra-violet radiation in photography, it is highly desirable to have a lens that provides good image quality and has relatively high light-gathering power. It is an object of this invention to provide a lens that satisties these requirements.

The lens according to this invention is of the general type having three components known as a triplet; that is, a three-component lens wherein convergent components sandwich a divergent component with air spaces therebetween. In applying this general three-component lens to refracting ultra-violet light, the rear component is divided into three separate elements to compensate for the dilerence in a h at which the lens isto operate. rear component of the triplet into three elements allows correction of the residual chromatic aberrations in the ultra-violet region without interfering with the correction for monochromatic aberrations. Because ultra-violet light or radiation having relatively short wavelengths will be partially absorbed by ordinary optical glass,

the refracting materials used are fused quartz and lithium. fluoride which have indices of re aci n and dispersion or providing proper correction in the ultra-violet wavelength region of the spectrum. With this arrangement it is possible to provide a lens having a high light-gathering power (f/2.5) which has been highly corrected for both chromatic and monochromatic aberrations.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of ythe invention and the best mode which has been contemplated of applying that principle.

In the drawings:

FIG. 1 is a diagrammatic sectional view of an ultraviolet lens according to this invention having an aperture of f/2.5;

FIG. 2 is a chart containing constructional data on one specific example of a lens constructed in accordance with this invention; l

FIG. 3 shows the transverse aberrations of the axial bundle;

FIGS. 4 and 5 show the tangential image height error;

FIG. 6 shows the astigmatic correction; and

FIG. 7 shows the residual distortion.

As shown in FIG. l, the lens, which may be considered as a divided rear component triplet corrected in the ultraviolet region of the spectrum, contains a ilat quartz protecting plate L1 which is separated and spaced from the single element converging iirst positive component of the triplet, IQ. Element L2 is constructed of lithium fluoride. Middle dispersing component is a single element lens L3 constructed of quartz. The divided rear component of the triplet consists of three separate spaced elements L4, L5, and L6. L4 is a positive meniscus of lithium uoride, L5 is a double convex lithium fluoride lens, and La is a negative meniscus of quartz.

The ilat quartz plate L1 is for the purpose of protecting the lithium fluoride element L2 as lithium uoride is slightly water-soluble and requires protection in humid envi- 3,035,490 Patented May 22, 1962 ronments. Elements L2 and L3 function in a manner somewhat similar to the tirst two elements of a conventional triplet with the exception that they are constructed of materials having indices of refraction and dispersions which will provide proper correction in the ultra-violet wavelength region. The rear component consisting of elements L4, L5, and L6 corrects the residual chromatic aberrations to provide tine image quality without introducing severe monochromatic aberrations which would be the case if a single element rear component were used. A single element middle dispersing component would not produce enough chromatic overcorrection. Therefore, the rear component is split into what might be considered a singlet L, and a doublet L5 and Ls. In this manner, the chromatic aberrations may be balanced while retaining correction for the monochromatic aberrations.

The constructioual data for a practical example of a lens having high light-gathering power, an aperture of f/2.5, is given in FIG. 2. This data is as follows:

In this table as in the drawings, the lens elements are numbered in order from left -to right and front to rear in the tirst column. N indicates the index of refraction for the sodium line of the refractive elements, and V indicates the conventional dispersive indices. The radii listed in column 4 are for the radii shown in FIG. 1, a plus sign denotes the center of curvature lies to the right of the lens surface and a minus sign indicates that the center of curvature lies to the left of the surface. The fourth column includes the thicknesses T of the various elements and the air spaces S between the elements as indicated in FIG. l. This lens when used at infinity with ultraviolet light has a relative aperture of f/2.5 and when used at a minifcation of 5 to l as designed for in the present example, produces an image of high quality having very little residual aberration. The lens is corrected for chromatic and monochromatic aberrations in the ultra-violet region of the spectrum. The constructional data given above is for a lens designed to work in the ultra-violet region of the electromagnetic spectrum, for example, in the region of 2300 to 2700 angstrom units and provides a 5 To'fmi''iii'czfin. The iield covered by this lens is locatH'TgTFt'nches before the front surface and is 5 inches in diameter. These figures imply a half icld angle of approximately 7. This lens may be used at other conjugates without noticeable loss of definition. Although the lens was designed to operate at a fixed fractional magnification, its correction is good enough to allow it to be used over a wide range of fractional magnification.

The corrections obtained with this design are shown in 3 FIGS. 3 `through 7. Referring to these figures, the following symbol denitions apply:

H=height of object in millimeters at 19.6 inches from lens TA=transverse aberrations in microns along the optical axis AH^=tangential image height errors in microns H=image height in millimeters X'v=amount of tangential and sagittal astigmatic errors in millimeters p.=microns A tan U '=slope of rays emerging from lens towards image plane mm.=millimeters While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. An optical lens having a relative aperture of f/ 2.5 and being highly corrected for aberrations in the ultraviolet range of the electromagnetic spectrum, said lens being constructed substantially according to the specification set forth in the following table:

wherein column 1 contains the separate lens elements, column 2 contains the refractive indices for the sodium line, column 3 contains the dispersive indices, column 4 contains the radii (R3-R12) of the lens surfaces, a plus sign indicating the center of curvature to the right of the surface and a minus sign indicating the center of curvatures to the left of the surface, the tifth column containing indications of the thicknesses (T1 to T8) of the lens elements and the air spaces (S1-S5) between the lens elements in inches.

2. An optical lens having a relative aperture of f/2.5 and being highly corrected for aberrations in the ultraviolet range of the electromagnetic spectrum, said lens being constructed substantially according to the specification set forth in the following table:

wherein column 1 contains the separate lens elements, column 2 contains the refractive indices for the sodium line, column 3 contains the dispersive indices, column 4 contains the radii (R3-R12) of the lens surfaces, a plus sign indicating the center of curvature to the right of the surface and a minus sign indicating the center of curvature to the left of the surface, the fifth column containing indications of the thicknesses (T2-T6) of the lens elements and the air spaces (S2-S5) between the lens elements in inches.

References Cited in the file of this patent UNITED STATES PATENTS 1,540,752 Bielicke June 9, 1925 1,541,407 Spangenberg June 9, 1925 1,580,751 Merte Apr. 13, 1926 2,085,437 Michelssen June 29, 1937 2,416,032 Warmisham et al Feb. 18, 1947 2,493,110 Corman Jan. 3, 1950 2,561,077 Tilton July 17, 1951 2,571,307 Taylor Oct. 16, 1951 2,645,155 Tronnier July 14, 1953 FOREIGN PATENTS 847,600 France July 3, 1939 OTHER REFERENCES On Lithium Fluoride-Quartz Achromatic Lenses# Stockbarger and Cartwright: Articles, pages 29, 30, 31, and Lithium-Fluoride Quartz Apochromat, pages 350, 351 of the Journal of Optical Society of America, vol. 29, January and August 1939. 

